1. Field of the Invention
The present invention relates to a method of designing an optical network telecommunication system, and specifically to an optimal accommodation design method for accommodating diverse client signals such as a synchronous optical network (SONET) signal and fiber channel signal in a wavelength division multiplexing (WDM) optical network.
2. Description of the Related Art
In recent years, an optical transmission and reception card (commonly called such as “ADM on λ” and “ADM on a card”) integrally incorporating a SONET signal (refer to ANSI T1.105 recommendation: Synchronous Optical Network Basic Description Including Multiplex Structures, Rates and Formats), an add/drop function of an SDH signal (refer to ITU-T Recommendation G.803: Architecture of Transport Networks Based on the Synchronous Digital Hierarchy), and a transponder function for an optical signal has been developed. Accordingly, a buildup of an upper layer network accommodating diverse client signals, such as SONET signal, SDH signal (named as “SONET/SDH signal” hereinafter), Ethernet (Registered Trademark) and fiber channel, on a WDM optical network structured by a WDM transmission apparatus has been made possible.
The present invention focuses especially on a design technique for accommodating a client signal accommodated in a SONET/SDH ring network built on a WDM optical network to a SONET/SDH frame.
FIG. 1 is a diagram describing a configuration change of a WDM apparatus. A WDM net and a SONET/SDH net built thereon have conventionally been structured by independently different apparatuses, that is, a WDM apparatus and a SONET/SDH ADM (Add/Drop Multiplexing) apparatus. The WDM apparatus is one performing a wavelength division multiplexing by overlapping an optical signal on different wavelength lights, while the SONET/SDH ADM apparatus is one for applying a time division multiplexing to a client signal of each channel and overlapping it on a single wavelength light. The purposes of design for accommodating a client signal on a network are to accommodate the entirety of the given client signals and also to minimize the number of SONET/SDH apparatuses and the associated apparatus cost. In the case of accommodating a client signal by using a SONET/SDH ADM apparatus, the accommodation has conventionally been carried out so as to increase a band usage ratio of each optical signal by considering a bandwidth of each client signal. The number of client signal ports of a SONET/SDH ADM apparatus is generally large, not requiring a consideration of the number of client signals per optical signal, and therefore a combination maximizing a band usage ratio has been selected in priority regardless of the number of client signals. That is, the conventional accommodation design has been able to provide the entirety of the client signals with interfaces for the number of ports that is capable of accommodating a natural number of client signals obtained by the following expression (1):(Number of ports on the client signal side)=(optical signal bandwidth of SONET/SDH ADM apparatus)/(bandwidth of one client signal)  (1)
Recent years, however, have been seeing that an ADM function 107 (refer to TRPN 108 in FIG. 1) of a SONET/SDH signal is integrally incorporated into the optical transmission/reception card 106 (which is indicated by a TRPN in FIG. 1) of a WDM apparatus which used to provide only a transponder function of an optical signal as shown on the right side of FIG. 1. This has made it possible to build up a SONET/SDH ring network (i.e., a synchronous digital signal net) in addition to a WDM net only by using a WDM apparatus.
Referring to the right side of FIG. 1, when accommodating a client signal by using an optical transmission/reception card 108, a difference from the case of using the SONET/SDH ADM apparatus is that the number of client signal ports of the optical transmission/reception card 108 is small, that is, up to approximately ten ports at most. Therefore, different from prior times, there are client signals expressed by:(Signal bandwidth of optical signal of an optical transmission/reception card)/(the number of add/drop ports of client signals of an optical transmission/reception card)<(bandwidth of a client signal)  (2); and expressed by(Signal bandwidth of optical signal of an optical transmission/reception card)/(the number of add/drop ports of client signals of an optical transmission/reception card)≧(bandwidth of a client signal)  (3).
FIG. 2 exemplifies a case of different results of accommodating a client signal between the cases of using the SONET/SDH ADM apparatus and WDM apparatus and that using the WDM apparatus equipped with an optical transmission/reception card. In the case of FIG. 2, four 2.5G channels, four 1.25G channels and eight 620M bps channels are accommodated in 10 Gbps bands with corresponding wavelength. Here, the number of client ports of the optical transmission/reception cards is eight. Here,(Bandwidth of an optical signal)/(the number of add/drop ports of client signals)=1.25 Gbps,
so that the client signals satisfying the expression (2) and those satisfying the expression (3) coexist. Only thing what the conventional design using the SONET/SDH ADM apparatus shall achieve is to maximize only a usage ratio of a total band, and therefore the accommodation is carried out in a descending order of band, resulting in generating two optical signals as shown in FIG. 2 (A). In the case of carrying out an accommodation by the optical transmission/reception card likewise by considering only a band usage ratio, however, three pieces of optical transmission/reception cards are necessary as shown in FIG. 2 (B), thus unable to accomplish an optimal accommodation by two pieces of cards as shown in FIG. 2 (C). This is because the conventional method does not consider a limitation of the number of client side ports of the optical transmission/reception card.
Further descriptions on the problems of the conventional optical network design method are provided here. The conventional design of a SONET network accommodates a pair of client signals having the same signal direction (i.e., bidirectional and unidirectional) as a client side protection type in the same optical transmission/reception card. However, more recent optical transmission/reception card furnished with an ADM on λ enables an accommodation of a pair of client signals having different client-side protection types or signal directions between a single pair of optical transmission/reception cards. Therefore, the conventional design method has been faced with the problem of being unable to accomplish an accommodation design of mixing optimal client signals in an optical transmission/reception card.
Also, when building up a SONET/SDH ring network on a WDM mesh network by using an optical transmission/reception card, the conventional method uniquely selects a ring path for accommodating each client signal prior to carrying out an accommodation design, followed by carrying it out. However, there is a possible problem of resulting in an absence of optimal design for a client signal that can take either of a plurality of ring paths because a ring path for accommodating a client signal is fixed in advance.
The problems associated with the optimal accommodation design as described above resembles the problem of an optimal resource allocation for example. For such a conventional technique, a patent document 1 has disclosed a technique having an apparatus in need of using a shared resource bid for a required volume and price of the resource and allocating the resource corresponding to the bid. And a patent document 2 has disclosed a search method for an optimal portfolio for improving a probability of gaining a high profit.
Even the use of such conventional techniques, however, has not been able to solve the problem of not capable of accomplishing an optimal design for accommodating a client signal by an optical transmission/reception card corresponding to client signal demands having different bandwidths, client side protections and signal directions.
[Patent document 1] Published Japanese translations of PCT international publication for patent applications No. 2003-520496 “Resource allocation”
[Patent document 2] Laid-Open Japanese Patent Application Publication No. 2000-293569 “Portfolio presentation method, presentation apparatus and a storage medium for computer program”